Integrated circuits, the key components in thousands of electronic and computer products, are interconnected networks of electrical components fabricated on a common foundation, or substrate. Fabricators typically build the circuits layer by layer, using techniques, such as doping, masking, and etching, to form thousands and even millions of microscopic resistors, transistors, and other electrical components on a silicon substrate, known as a wafer. The components are then wired, or interconnected, together to define a specific electric circuit, such as a computer memory.
One important concern during fabrication is flatness, or planarity, of various layers of the integrated circuit. For example, planarity significantly affects the accuracy of a photo-imaging process, known as photomasking or photolithography, which entails focusing light on light-sensitive materials to define specific patterns or structures in a layer of an integrated circuit. In this process, the presence of hills and valleys in a layer means that various regions of the layer will be in or out of focus and that certain resulting structural features in the layer will be smaller or larger than intended. Moreover, hills and valleys can reflect light undesirably onto other regions of a layer and add undesirable features, such as notches, to desired features. These problems can be largely avoided if the layer is sufficiently planar.
One process for making surfaces flat or planar is known as chemical-mechanical planarization or polishing. Chemical-mechanical planarization, often called CMP for short, typically entails applying a fluid containing abrasive particles to a surface of an integrated circuit, and polishing the surface with a rotating polishing head. (In some instances, both the surface and the polishing head rotate.) The mixture of the fluid and abrasive particles is known as a slurry. The polishing head typically includes several holes, known as slurry dispensers, which dispense the slurry onto the surface during polishing. After polishing, a gas, such as air or nitrogen, is forced through the slurry dispensers to facilitate separation of the polished surface from the polishing head.
One problem that the inventor recognized with this planarization method is that forcing air or nitrogen through slurry dispensers immediately after polishing occasionally dries slurry on the polished surface, causing particles in the slurry to stick to the polished surface. Although the polished surface is sometimes rinsed following the polishing process, some of the particles remain on the polished surface as defects. Accordingly, there is a need for a chemical-mechanical planarization technique that reduces the chance of these defects.